1. Field of the Invention
The present invention relates to a honeycomb structure for use in a filter for trapping/collecting particulates in an exhaust gas of an internal combustion engine, boiler, and the like, a method for manufacturing the honeycomb structure, and an exhaust gas purification system using the honeycomb structure.
2. Description of the Related Art
An exhaust gas exhausted from internal combustion engines such as a diesel engine contains a large amount of particulates (particulate materials) containing carbon which causes pollution as a major component. Therefore, a filter for trapping/collecting the particulates is sometimes mounted in an exhaust system.
In general, as a filter to be used for this purpose, as shown in FIGS. 6(a) and (b), one usually uses a honeycomb structure including: a plurality of through channels 9, porous partition walls 7 separating the through channels one another; said through channels extending through an axial direction of the honeycomb structure; and the plugging portions 11 plugging the predetermined through channels 9a at one end face, and the rest of the through channels 9b at other end face opposite to the plugged end of predetermined through channels 9a. 
The exhaust gas flows in the filter made of such a honeycomb structure mentioned above via one end face 3 thereof, and the gas flows out of the other end face 5 after the particulates included in the gas are removed. Concretely, the exhaust gas first flows into the through channels 9b whose ends are not plugged at the end face 3 on an inflow side and whose other ends are plugged face 5 on an outflow side, moves into the through channels 9a whose ends are plugged at the end face 3 on an inflow side and whose ends are not plugged at the end face 5 on an outflow side, via the porous partition walls 7, and flows out via the through channels 9a. Moreover, in this case, the partition walls 7 function as filter layers, and the particulates in the exhaust gas are trapped by the partition walls 7 and deposited on the partition walls 7.
After the use of the filter for a given period of time, the particulates deposited in the filter are burnt with heating the filter by electric conduction of an electric heater to be removed, but are not completely removed, and some of the particulates remain as ashes (ash components) in the filter. Therefore, with the use of the filter over a long period of time, a filter capacity substantially decreases by the deposition of the ashes, pressure loss increases, and an amount of particulates that can be trapped/collected decreases. There has therefore been a problem that the frequency for the regeneration treatment of the filter by burning/removing the captured particulates as described above have to be increased.
To solve the problem, for example, there has been proposed an apparatus in which the filter is supported in a direction vertical to the direction of the gas flow, and said apparatus having a vibration device provided to the filter, and an ash collecting portion provided at lower portion of the filter for collecting ashes dropping off the filter by virtue of vibration applied to the filter by the vibration device (see JP-A-8-28247).
Moreover, there has been proposed a method in which a highly pressurized fluid such as water is sprayed onto one end of the filter to clean/remove the residue after burning resided in the filter (see JP-A-2001-50028).
Furthermore, in the same manner as in the present application, there has been proposed a method for forming a through-hole in the plugging portion at the end of the through channel to discharge the ashes (see Japanese Utility Model Application Laid-Open No. 58-72414).
However, any one of these techniques proposed has not been very practical. For example, the device proposed in the above-mentioned Laid-open Japanese Utility Model Application can not be used practically since a trapping/collecting efficiency of particulates during the use is low because the through-hole formed in the plugging portion is not closed by the trapped particulates. Moreover, a special mechanism or apparatus is required to remove the ashes from the filter, in some case, or the filter needs to be detached from the exhaust system in other case to remove the ashes from the filter. Therefore, the conventional techniques or methods have not been practical.